/*
 * Copyright (C) 2007 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import java.util.Collection;
import java.util.Set;
import javax.annotation.Nullable;

/**
 * A set which forwards all its method calls to another set. Subclasses should override one or more
 * methods to modify the behavior of the backing set as desired per the
 * <a href="http://en.wikipedia.org/wiki/Decorator_pattern">decorator pattern</a>.
 *
 * <p>
 * <b>Warning:</b> The methods of {@code ForwardingSet} forward <b>indiscriminately</b> to the
 * methods of the delegate. For example, overriding {@link #add} alone <b>will not</b> change the
 * behavior of {@link #addAll}, which can lead to unexpected behavior. In this case, you should
 * override {@code addAll} as well, either providing your own implementation, or delegating to the
 * provided {@code standardAddAll} method.
 *
 * <p>
 * <b>{@code default} method warning:</b> This class does <i>not</i> forward calls to {@code
 * default} methods. Instead, it inherits their default implementations. When those implementations
 * invoke methods, they invoke methods on the {@code ForwardingSet}.
 *
 * <p>
 * The {@code standard} methods are not guaranteed to be thread-safe, even when all of the methods
 * that they depend on are thread-safe.
 *
 * @author Kevin Bourrillion
 * @author Louis Wasserman
 * @since 2.0
 */
@GwtCompatible
public abstract class ForwardingSet<E> extends ForwardingCollection<E> implements Set<E> {
    // TODO(lowasser): identify places where thread safety is actually lost

    /** Constructor for use by subclasses. */
    protected ForwardingSet() {}

    @Override
    protected abstract Set<E> delegate();

    @Override
    public boolean equals(@Nullable Object object) {
        return object == this || delegate().equals(object);
    }

    @Override
    public int hashCode() {
        return delegate().hashCode();
    }

    /**
     * A sensible definition of {@link #removeAll} in terms of {@link #iterator} and
     * {@link #remove}. If you override {@code iterator} or {@code remove}, you may wish to override
     * {@link #removeAll} to forward to this implementation.
     *
     * @since 7.0 (this version overrides the {@code ForwardingCollection} version as of 12.0)
     */
    @Override
    protected boolean standardRemoveAll(Collection<?> collection) {
        return Sets.removeAllImpl(this, checkNotNull(collection)); // for GWT
    }

    /**
     * A sensible definition of {@link #equals} in terms of {@link #size} and {@link #containsAll}.
     * If you override either of those methods, you may wish to override {@link #equals} to forward
     * to this implementation.
     *
     * @since 7.0
     */
    protected boolean standardEquals(@Nullable Object object) {
        return Sets.equalsImpl(this, object);
    }

    /**
     * A sensible definition of {@link #hashCode} in terms of {@link #iterator}. If you override
     * {@link #iterator}, you may wish to override {@link #equals} to forward to this
     * implementation.
     *
     * @since 7.0
     */
    protected int standardHashCode() {
        return Sets.hashCodeImpl(this);
    }
}
